Method for recovering oil from oil-bearing minerals



Jan. 22, 1963 1.. D. FRIEDMAN 3,074,877

METHOD FOR RECOVERING OIL FROM OIL-BEARING MINERALS Filed July 1. 1959 2 Sheets-Sheet 1 T'ICIJ- 7 Jan. 22, 1963 1.. D. FRIEDMAN METHOD FOR RECOVERING OIL FROM OIL-BEARING MINERALS 2 Sheets-Sheet 2 Filed July 1. 1959 -iuP United States Patent 3,074,877 METHOD FOR RECOVERING OIL FROM OIL-BEARING MINERALS Louis D. Friedman, Beacon, N.Y., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware Filed July 1, 1959, Ser. No. 824,301 8 Claims. (Cl. 208-11) This invention relates to an improved process for the recovery of oil from oil-bearing minerals. Various oilbearing minerals for example oil shale, oil sand, and tar sand may be treated by the process of the invention. The process is particularly applicable to the recovery of oil from oil shale.

In carrying out the process of this invention, an oilbearing mineral is subjected to treatment with carbon di oxide at a pressure in the range of 1000 to 3000 pounds per square inch gauge or higher and at a temperature in the range of about 700 to 900 F. for a period of about 20 minutes to 6 hours, preferably 30 minutes to 2 hours.

It is known that certain oil-bearing minerals, particularly oil shales, contain substances known as kerogens which may be converted to hydrocarbon oil by the application of heat. Various methods have been proposed hereinbefore for the recovery of hydrocarbon oil from oil shales, For example, it has been proposed heretofore to recover shale oil from oil shale by contacting the shale with steam at temperatures above 850 F. and at substantially atmospheric pressure. It has also been proposed to retort oil shale in the presence of various gases, including carbon dioxide. It has been proposed heretofore to recover oil from oil shale by treatment with carbon dioxide, either in substantially pure form or admixed with other gases, such as hydrogen. Generally such processes are carried out at pressures below about 100 pounds per square inch gauge and at temperatures above about 900 F. The present process has some advantages over prior proposals as will be evident from the following detailed description of the process.

Other oil-bearing minerals, such as oil sands or tar sands, contain hydrocarbons which may be extracted from the mineral residue or displaced by means of liquid, particularly at elevated temperatures. The present process may be applied also to these materials.

One major disadvantage of prior processes for the recovery of oil from oil shale in the presence of carbon dioxide is the high heat requirements which are due at least in part to the decomposition of carbonates contained in the oil shale. A large part of the heat required in conventional shale retorting processes is required for decomposition of the carbonates. Carbon dioxide liberated from the carbonates generally serves no useful purpose in the retorting process. The decomposition of carbonates is largely prevented in the present process by the combination of the relatively low temperature at which the retorting is conducted and the carbon dioxide partial pressure in excess of 1,000 pounds per square inch.

The process of this invention will be more readily understood from the following detailed description, taken in conjunction with the accompanying drawing.

FIG. 1 illustrates diagrammatically an arrangement of apparatus suitable for carrying out the present process in a continuous retort.

FIG. 2 illustrates diagrammatically an arrangement of apparatus suitable for carrying out the present process in a series of batch type retorts.

With reference to FIG. 1, oil bearing mineral of a suitable particle size, generally not larger than about 1 inch maximum diameter and preferably not larger than about "ice inch maximum diameter, is charged to a mixer 1 where it is mixed with sufficient water to form a pumpable mixture. Suflicient water is required to fill all the void spaces between the solid particles and completely immerse the solid in water. Approximately equal parts of water and solid by Weight are generally preferred.

Alternatively, oil may be used in place of water in the preparation of the feed mixture. The liquid used in preparing the feed mixture may be preheated prior to contact with the oil shale, heated while in contact with the oil shale, or the mixture of liquid and oil shale or other oil-bearing minerals may be charged into pressurized lock hoppers and the mixture heated to the desired temperature prior to introduction to the retorting zone. Some of the liberation of the oil from the oil bearing mineral and particularly some of the conversion of kerogen in oil shale to hydrocarbon oil may be accomplished by the heat treatment in the presence of the feed liquid. With water as the feed liquid, some hydration of the shale may take place at the elevated pressure. With oil as the feed liquid, there may be disintegration of the shale particles.

When oil shale is treated, we have found, that particles smaller than about A inch in average diameter are not particularly advantageous, insofar as the time required for the recovery of shale oil from oil shale is concerned. Smaller particles are, however, somewhat more readily handled as a suspension in water, and may be preferred for this reason. Usually, it is desirable to crush the oil shale only to the extent necessary to permit the shale particles to pass without plugging through the lines and valves required for charging the shale to the retorting vessel in accordance with the method described herein. It is generally preferable to crush the shale to the extent necessary to permit the shale particles to pass through a sieve or screen having openings of about inch and to utilize the unclassified material passing through the screen as feed to the process.

Solid particles in water are withdrawn from mixer 1 to a pump 2 from which the mixture is passed at elevated pressure within the range of 1,000 to 3,500 pounds per square inch gauge into the lowermost portion of a retorting vessel 3. Heater 4 is optionally provided to preheat the mixture, suitably to a temperature Within the range of about 300 to 650 F. and below the boiling point of water at the existing pressure. This heater may take the form of an externally heated tubular coil set in a furnace or other suitable heater.

When a watery mixture is preheated, it is sometimes desirable, particularly with oil shales, to add an alkali metal hydroxide, preferably sodium hydroxide, to the water used in the preparation of the feed mixture. An alkali metal carbonate also may be added to the water to supplement the action of the alkali metal hydroxide. A preferred treatment involves addition of both alkali metal carbonate and alkali metal hydroxide to the water used in the preparation of the feed mixture. Generally, sufiicient sodium hydroxide is added to the water to bring the pH within the range of 9 to 10. A quantity of sodium carbonate is added which is sulficient to precipitate calcium remaining in the solution in the shale-water mixture and reduce the calcium hardness of the Water (expressed as calcium carbonate) to 0 to 2 parts per million. The calcium is precipitated as insoluble calcium carbonate which is deposited on the solid shale particles and passes through the heater with the solid particles without forming deposits on the heater walls.

The solid water mixture is charged into the lowermost portion of retorting zone 3. The retorting zone is designed to maintain a bed of solid particles in contact with the retorting gas and at a temperature in the range of 700 to 900 F, preferably 800 to 900 F., for a period of time within the range of about 20 minutes to about 3 hours. As additional solid is fed into the bottom of the retort, the solid particles already in the retort are displaced upward and overflow through discharge conduit 6. Shale particles Withdrawn from the retort through outlet pipe 6 are discharged from the retorting vessel, suitably to a suitable lock hopper arrangement well known in the art of handling solids at high pressure.

Carbon dioxide of at least 90 percent purity by volume is introduced into the upper portion of the retorting vessel 3 through line '7 at a pressure within the range of 1000 to 3500 pounds per square inch gauge and at a temperature sufiicient to maintain a temperature of the solid particles in the major portion of the bed of solid particles contained within the retort 3 within the range of 700 to 900 F. It is necessary to heat the incoming retorting gas to a temperature somewhat above the temperature desired in the bed, generally within the range of 850 to 950 F. As the retorting gas passes downwardly through the bed of solid, oil-bearing particles, oil liberated from the solid is carried in the gas in vapor or liquid form to the lower portion of the retort. Retorting gas containing some hydrocarbon oil vapors from the oilbearing mineral is discharged from the vessel through line 8. After the recovery of hydrocarbon from the retorting gas, and purification if desired, carbon dioxide may be recycled to the retort. Carbon dioxide feed rates of the order of 5,000 to 100,000 standard cubic feet per ton of oil shale per hour may be used. Carbon dioxide consumption is usually negative; some carbon dioxide is liberated from the shale during the retorting process. Oil and water are drawn from the retort through line 9. The oil-water mixture may be passed to a suitable auxiliary separator, not shown in the drawing, where the oil is separated from the water and recovered as a product of the process. If desired, efiluent gas, water, and recovered oil may all be withdrawn from the retort through a common outlet in the lower portion of the retort.

FIG. 2 of the drawings illustrates diagrammatically an arrangement of apparatus for carrying out a batchwise retorting operation in a series of retorts in accordance with the present invention. This operation is particularly applicable to retorting oil shale. As illustrated, pressure vessels A, B, C, D, E and F are arranged for treatment in sequence in the order illustrated. Connecting lines are arranged so that the various pressure vessels may be connected in a cyclic manner to provide the how pattern illustrated in the figure. It is to be understood that neither the specific arrangement illustrated nor the specific number of vessels is to be construed as limiting the present invention.

In operation, retort A is charged, or recharged, with solid oil bearing mineral, for example oil shale, while the remaining retorts are connected for gas circulaation. For convenience, the operation will be described as applied to oil shale. Residue from a various retorting operation is discharged from retort A and fresh oil shale in the form of particles no larger than about 2 inches in average diameter is charged to the retort. After a retort has been charged with fresh oil shale, the charge is preheated by circulation of hot gases through the retort. Preheating of the freshly charged shale may be accomplished in any of a number of ways. in the specific embodiment illustrated in FIG. 2, preheating of the oil shale is accomplished by circulating hot carbon dioxide over the .fresh oil shale. This carbon dioxide is heated by contact with hot residual shale resulting from the retorting operation. In this particular example, the retorting operation proper is carried out in retort D. Retorts B and. C contain fresh shale undergoing preheating while retorts E and F contain residual solids undergoing cooling. To preheat fresh shale in retort B, carbon dioxide is passed over spent shale in retort F where the carbon dioxide is heated and then passed over the fresh shale in retort B. Gas discharged from retort B is recirculated to retort F. Similarly, partially heated shale is further heated in retort C by circulation of carbon dioxide in a closed cycle through retorts C and E.

Carbon dioxide from a suitable source, preferably containing at least percent carbon dioxide by volume, is introduced to the system as required through line 2 1 to compressor 2?, from which the carbon diomde-rich gas is passed through heaters 23' and 24- to retort D. Carbon dioxide is delivered fromheater 2 1 to retort D at a temperature in the range of about 750 to about 950 F. sufficient to raise the temperature of the shale in vessel D to a temperature within the desired range of 700 to 900 F. effective for the removal of hydrocarbon in vapor form from the shale. Recovery of oil from the shale is substantially complete when the temperature of the shale at the top of the retort reaches 300 F. Although generally satisfactory recovery may be obtained from any individual particle of the oil shale within a period of time of about 30 minutes at retortin-g temperatures above 800 F., the holding time or treating time in any given retort is somewhat longer and may range up to several hours depending upon the size of the vessel and the depth of the bed of solid contained therein.

Gaseous eiiluent from retort D containing hydrocarbon vapors, is passed through heat exchangers 25, 26 and 22 and through cooler 27 to separator 28. Gas and liquid are separated from one another in separator 28. Gas from separator 28 may be recycled directly via compressor 22, heat exchanger 23, and heater 24 of retort D.

Generally it is desirable to purify at least a portion of the recycle gas stream. This may be carried out in purification system 31. Purification may be effected by selective absorption or low temperature condensation of car bon dioxide from undesirable gaseous components of the gas stream. Water, light hydrocarbons, and aqueous solutions of amines or alkali metal carbonates are suitable absorbents for carbon dioxide and hydrogen sulfide and also permit separation of hydrogen sulfide from carbon dioxide. Normally, in the treatment of oil shale, the gas stream contains nitrogen, hydrogen sulfide and gaseous hydrocarbons. Gaseous hydrocarbons may be converted to carbon dioxide by reaction with oxygen or air and the carbon dioxide recovered from the resulting gas mixture utilized to remove the oil from the mineral.

Oil separated from the gas stream in separator 28- is discharged through line 29 for further processing, suitably by turbulent flow hydrogenation. A portion of the oil may be reacted with oxygen and steam to produce carbon monoxide and hydrogen. Carbon monoxide in the resultant hydrogen-carbon monoxide mixture may be then reacted with steam to produce carbon dioxide and additional hydrogen. After separation, the carbon dioxide may be used as retorting gas and the hydrogen used to treat the recovered crude shale oil. Heavy residue, i.e. heavy hydrocarbons boiling above about 700 F. at atmospheric pressure, from the hydrogenation may be sub ected to partial oxidation to produce hydrogen and carbon dioxide as described above.

Heat remaining in the solid mineral matter following retorting is used to preheat further amounts of oil shale prior to retorting. As illustrated in FIG. 2 preheating of the oil shale is carried out in two stages using circulating carbon dioxide in each stage. It is to be understood that the preheating may be accomplished in a single stage or in several stages without departing from the spirit of this invention.

Following preheat of the oil shale in retort B, as previously described, the shale is further preheated in retort C by circulating hot carbon dioxide over the shale. Carbon dioxide is first heated by passing it through retort E into contact with hot residue from previously retorted shale. Spent shale residue in retort E gives up heat to the carbon dioxide which, in turn, gives up its heat to the fresh shale particles in retort C. Heat from the retorted shale residue in retort E is transferred to fresh incoming shale in retort C. Heat exchanger 25, which is optional, may be used to further preheat the carbon dioxide leaving retort E and prior to its introduction to retort C. Circulation of carbon dioxide in a closed cycle through vessels C and E is accomplished by a suitable circulating blower or compressor 32. Make-up carbon dioxide may be supplied to vessels C and E as required from compressor 22 through line 33 as controlled by valve 34.

Partially cooled spent shale is further cooled in retort F by contact with cold carbon dioxide. The carbon dioxide stream heated in retort F is passed to retort B to preheat the fresh cold shale previously charged to retort B. Effiuent gas from retort B is relatively cold; this gas is recirculated by pump 35, preferably in a closed cycle, from retort B to retort F. Additional carbon dioxide as required is supplied to vessels B and F through line 33 as controlled by valve 36. Heat exchanger 25 optionally may be used to further preheat the efliuent gas from retort F prior to its introduction to retort B. Heat from the shale in retort F is transferred to the fresh shale in retort B. Additional heat supplied to the gas stream by optional exchanger 26, if employed, assists in preheating the fresh oil shale.

As a specific example, oil shale is charged to the retorting system of FIG. 2 at about 75 F. The shale is preheated in two successive heat exchange stages, as illustrated, to a mean temperature of approximately 515 F. The fresh shale is heated to a mean temperature of approximately 300 F. in the first heat exchange step and to about 515 F. in the second. Retorting is carried out with 900 F. carbon dioxide. No heat exchange is employed between the eflluent gas from the retort and the circulating heat exchange gas. Spent shale residue at a mean temperature of 850 F. is cooled in two successive heat exchange stages as illustrated, to approximately 575 F. and 300 F. respectively. Spent shale is discarded at a mean temperature of 300 F.

The retorting of the oil shale in vessel D is carried out at a pressure within the range of 1,000 to 3.500 pounds per square inch gauge. The heat exchanger or heat recovery, in the cycle made up of retorts C and E and in the cycle comprising retorts B and F may be at substantially the same pressure as that in retort D or the pressure in these closed cycles may be lower than in retort D. As a specific example retorting is carried out in the retort D at an average pressure of 2,000 pounds per square inch gauge, gas circulation through retorts C and E is carried out at an average pressure of 1,000 pounds per square inch gauge, and circulation through retorts B and F is carried out at an average pressure of 500 pounds per square inch gauge.

In the sequence illustrated, a period of time for each operation in the range of 20 minutes to one hour is usually adequate. It will be appreciated that the time requirements depend to some extent on the particle size of the oil shale and the depth of shale bed in each of the retorts. It will be evident that the larger size particles require longer heating times than do the smaller particles.

The process of this invention is further illustrated in the following examples reporting data from runs made in accordance with the invention described herein.

Colorado Oil Shale having a Fischer Assay of about 28.3 gallons per ton was crushed to a particle size of inch and smaller and treated with carbon dioxide under pressure under the conditions indicated in the following table. The results of these tests are compared with the Standard Fischer Assay as described in U.S. Bureau of Mines R1. 3977 (October 1946).

Fischer Example 1 Example 2 Example 3 Assay Temp, F 93. 2 700 700 700 Time, Hrs 2 1 6 6 6 Pres., p.s.i.g. 0 300 1,400 3,000 Percent Organic 1 Removed 84. 2 53. 8 80. 0 86. 7 Percent Organic carbon removed 80. 3 57. 2 77. 9 76. 4 Percent Carbon removed. 55. 6 41. 0 44. 9 52. 2 Gas analysis:

Hydrogen 6. 9 1. 3 0. 5 Methane 8. 0 2. 4 0. 8 Oz hydrocarbons. 2. 1 1. 2 0. 4 C3 hydrocarbons--." 3. 5 1. 5 0.6 Carbon dioxide 73. l 92. 6 96. 8 Nitrogen and Argon 6.0 0. 4 0.7 Hydrogen sulfide- 0. 3 0. 6 0. 2 Ammonia 0.1 Oil Analysis:

Percent Carbon 80. 3 85.0 Percent Hydrogen- 10. 4 11.5 Percent Nitrogen 2. 48 1 68 1. 71 Percent Sulfur 0.23 0.76 0. 79

1 Includes nitrogen, sulfur, oxygen. Total heating time.

The foregoing table illustrates the effectiveness of carbon dioxide treatment of oil shale at high pressure. Example 1, included for comparison purposes, shows that much poorer recoveries are obtained at the relatively low pressure of 300 p.s.i.g. as compared with pressures within the range of 1,000 to 3,500 p.s.i.g.

Obivously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method of processing oil-bearing minerals selected from the group consisting of oil shales, oil sands, and tar sands for the recovery of hydrocarbon oil therefrom by retorting with gas which comprises contacting said mineral in a treating Zone with carbon dioxide of at least volume percent purity at a temperature in the range of from about 700 F. to about 900 F. and a carbon dioxide partial pressure within the range of from about 1,000 to 3,000 pounds per square inch gauge, continuously passing said carbon dioxide over said mineral for a period of time within the range of 15 minutes to 6 hours sufiicient to cause substantially complete distillation of oil from said mineral, withdrawing said carbon dioxide containing oil vapors from contact with said mineral, and recovering oil from said withdrawn carbon dioxide.

2. A process according to claim 1 wherein said mineral is contacted with from about 5,000 to about 100,000 standard cubic feet of carbon dioxide per ton of mineral per hour.

3. A process according to claim 1 wherein oil bearing mineral in particle form is admixed with sufficient carrier liquid to form a pumpable mixture, said mixture is passed into the lowermost portion of said treating zone, carrier liquid is withdrawn from the lower portion of said treating zone substantially free from mineral particles where by mineral particles substantially free from said carrier liquid are displaced upward in said treating zone, treated solid particles are withdrawn from the upper portion of said treating zone, said carbon dioxide is introduced into said treating zone into contact with said mineral particles at a level above the point of withdrawal of said liquid, and eflluent gas and recovered hydrocarbons are withdrawn from said treating zone below the point of introduction of carbon dioxide and above the point of withdrawal of said carrier liquid.

4. A process according to claim 3 wherein said carbon dioxide is introduced to said treating zone above the point of discharge of treated solid particles therefrom, and effluent gas and recovered hydrocarbons are with- "Z drawn from said treating zone at a point immediately adjacent the point of withdrawal of said carrier liquid.

5. A process according to claim 3 wherein said carrier liquid is water heated prior to its introduction into said treating zone to a temperature not abovethe boiling point of water at the existing pressure in said treating zone.

6. A process according to claim 1 wherein a plurality of zones containing said mineral are employed and wherein said mineral is successively contacted with carbon dioxide wherein at least one ofsaid zones is said treating zone wherein said mineral is contacted with said carbon dioxide at a temperature in the range of from about 700 F. to about 900 F. and the others of said zones are heat transfer zones, the steps comprising circulating carbon dioxide in a closed cycle alternately into contact with treated hot solid particles of mineral residue in one of said heat transfer'zones effecting cooling of said solid and heating of said carbon dioxide, and thereafter passing carbon dioxide heated by said mineral residue directly into contact with fresh mineral in a second heat transfer zone at a temperature below the temperature in said treating zone whereby heat from said mineral residue is transferred directly to fresh'mineral prior to contact with carbon dioxide in saidtreating zone.

7. A process according to claim 6 wherein a plurality of said closed cycles are employed to progressively heat said fresh mineral prior to treatment in said treating zone and to progressively cool said treated mineral residue subsequent to treatment in said treating zone;

8. A process according to claim 6 wherein said heat transfer zones in which said mineral is heated and said mineral residue is'cooled by said closed cycle heat transfor with circulating carbon dioxide are maintained at superatmospheric pressure below 1000 pounds per square inch gauge.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3 O74 877 January 22 1963 Louis DO Friedman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 58 for 'cireulaation read an circulation line 60 for 'various read previous column 5 line 4:5 for "3500"" read 3 500 column 6 line 43, after "130 insert we about Signed and sealed this 6th day of August 1963,

(SEAL) Attest:

ERNEST w. SWIDER DAVID L- LADD Attesting Officer Commissioner of Patents 

1. A METHOD OF PROCESSING OIL-BEARING MINERALS SELECTED FROM THE GROUP CONSISTING OF OIL SHALES, OIL SANDS, AND TAR FOR THE RECOVERY OF HYDROCARBON OIL THEREFROM BY RETORTING WITH GAS WHICH COMPRISES CONTACTING SAID MINERAL IN A TREATING ZONE WITH CARBON DIOXIDE OF AT LEAST 90 VOLUME PERCENT PURITY AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 700* F. TO ABOUT 900* F. AND A CARBON DIOXIDE PARTIAL PRESSURE WITHIN THE RANGE OF FROM ABOUT 1,000 TO 3,000 POUNDS PER SQUARE INCH GAUGE, CON- 